libspf 1.0 API Documentation
The API is documented through the use of Doxygen and provides an extremely indepth portal into libspf. If you have never used Doxygen before you are in for a nice treat.
Additional documents authored outside of Doxygen are:
Debugging libSPF 1.0 - [PDF] or [TXT]

A comprehensive look at how debugging works in libSPF 1.0 and how you can make the best use of it.
libSPF 1.0 DNS Cache - [HTML]

An overview of the DNS Caching functionality that is available in the development line of libSPF. As of time of this writing the new development line has not been announced. Until such time as it is announced you can contact James Couzens and request a copy for testing. Once the announcement is made anonymous access to the CVS server will be made available.